BDS Overview

What is it?

The PRI BDS (Belt Drive System) is essentially two systems which can be used together or independently of one another in conjunction with commercial off the shelf bicycle pullies and belts. The first system is a IGH (Internally Geared Hub) – Thru Axle Conversion System or I–TACS for short. It allows a hub with a solid axle design (such as an internally geared hub) to be mounted onto a bicycle frame that utilizes a thru axle. The second system is a modular Bicycle Belt Drive Automatic Tensioning System or B-DATS for short. Just like the name implies it’s a belt tensioning system the applies adequate tension on the slack side of the belt throughout the rear suspension system’s full range of motion.

Are both systems patented?

Yes, both system are protected under Patent 12,103,641

What off the shelf components does the system utilize?

What are the materials of construction?

See overviews above

What’s so unique about this setup?

Let me start off by saying there is no other system like this on the market that is specific to conventional full suspension Mountain bikes. Yes there are manufactures who offer complete bikes with belt drive systems, however they offer purpose built bikes: see section below” Are there bike manufacturers that offer belt drives on Full Suspension Mountain bikes?”

First, the Shimano range of Internally geared hubs are only offered in a solid axle design with 135mm spacing and were never intended to be used for MTB applications. This was a big hurdle to overcome since newer high-end mountain bikes utilize a Thru -Axle with 135/142/148 mm rear spacing. In turn I had to develop the components and installation method to be able to mount and install the hub.

Typical Solid Axle IGH Install (Drive Side)

Typical Solid Axle IGH Install (Non-Drive Side)

Second, a belt tensioner for this type of application did not exist. In fact, Gates does not offer a belt tensioner of any kind. Therefore, I had to develop a tensioner from scratch that could accommodate the significant chain-stay length growth seen in 100+ mm travel mountain bikes. There are now two variations of the tensioner: Modular Mounted and Universally Mounted. The modular mounted is specific to the I-TACS and Alfine/solid axle hubs and is meant to be pair with OEM specific hanger adapters, while the Universally Mounted version will work work with any hub and almost any bicycle that utilizes a standard derailleur hanger.

B-DATS Tensioner Assembly **(Modular Mount)**

B-DATS Tensioner Assembly (**Universal Mount)**

Third, a customer cable holder had to be developed for the Rocky Mountain Thunder Bolt as the stock Shimano cable holder is long and interferes with the belt and chain stay. The custom cable holder is super compact and should work with most of the bikes on the market.

PRI Cable Holder 2019 Rocky Mountain Thunderbolt

What other brand hubs can the tensioner be used with?

Enviolo
Kindernay
Rohloff

Can the tensioner accommodate different size rear sprockets?

Yes, The Universal Mount version will accommodate 19-22T rear sprockets. The Modular mount is currently specific to 22T sprockets.

How much chain-stay growth can the tensioner accommodate?

It can theoretically accommodate up 35mm (1.38″) of chain stay growth.

What belt/chain line will the tensioner accommodate?

45.5mm (with 135/142 mm rear spacing using 3 mm offset Mounting Clamp)
52mm (with 148 mm rear spacing using 3 mm offset clamp)
55mm (with 142 mm rear spacing 0 mm offset clamp)

What’s so great about it?

It makes the overall riding experience that much better. You really have to experience to fully understand and appreciate it, but her It goes:

You don’t have to pedal to shift through the gears. (Believe it or not, this is a huge benefit, for both beginner and experienced riders)
Virtually silent
Belt requires no lubrication
Belt will outlast a chain setup by 4-10 times
The IGH will most likely outlast the bike (provided it’s not abused and maintained. I have heard of some people getting 20,000 miles out of them)
Requires far less maintenance than conventional derailleur/chain systems
No chain slap. No more broken, dropped, or derailed chains.
More ground clearance – The swing arm is significantly shorter than a 1x 11/12 derailleur and typically rests higher in the swing/rotational path
Can be adapted to almost any conventional MTB
Shifting is smooth, reliable, and repeatable

What’s not so great about it?

You must have a way to get the belt onto the rear triangle. Most Full suspension have a third pivot in the rear triangle which facilitates this, however most of the small travel full suspensions are doing away with the third pivot. and there are a handful of other that use a one piece rear triangle. Unfortunately bikes with a one-piece rear triangle cannot utilize this setup.
You cannot shift the gears under load (hard pedaling or standing up while pedaling). If you do the hub will most likely fail. This is something you just have to get used to and get into the habit of not pedaling for a split second before you shift. You would be surprised how quickly you do. I have been riding Internally geared hubs since 2013 without incidents, and for me it has become second nature.
Since the hub utilizes a solid axle, the rear wheel has to be removed using a certain method of which includes removing the caliper and deflating the rear tire. (I will post a video soon of the complete process).

What bikes has the system been installed on?

Currently the system has been fitted onto:

2017 Specialized Epic FSR w/Alloy Frame
2019 Rocky Mountain Thunderbolt w/Full Carbon Frame
2020 Scott Genius Ultimate
2021 Watt Wagon Hydra eMTB

Will this setup fit on other bike brands?

Yes, however fitment must be verified for each case. This is because every manufacturer is different and there are multiple factors to be considered:

Chainring clearance between the chain-stay and sprocket varies between manufacturer. The Gates sprockets are reasonably wider than standard chainrings (see pic below).
Although most manufactures have standardized on a Thru axle system, some follow the Syntace standard while others use a hybrid between the standard and their own design.
The interface to mount the derailleur hanger is different for each manufacturer, therefore a custom hanger adapter which is required to mount the modular tensioner, must be designed for each manufacturer.
As noted in one of the previous sections. You must have a way to get the belt onto the rear triangle. Most Full suspension have a third pivot in the rear triangle which facilitates this. Unfortunately frames with a one-piece rear triangle cannot utilize this setup.

How long has the system been tested?

I have been running the IGH setup (without the belt drive system) on Black Widow since 2017 without any issues. I added the belt drive system in November of 2019.

Red Thunder has had the complete system installed since June of 2020.

Scotty has had the complete system installed since the beginning of September of 2021.

I estimate that I have about 400 hrs of testing between all three bikes without issues.

What’s the cost for this setup?

Belt – $75
Rear Pulley – $80-108 (Depends on OEM fitment and tooth count)
Front Pulley -$60 (for 39 Tooth)
NSB Spider – $70
Alfine 11 Speed Shifter – $85
Alfine 11 Speed Hub -$400
B-DATS (Belt Tensioning System) -$600 (Unfortunately for the time being these are made in small batches plus price for machined components has doubled since COVID. If there is more demand I can make in larger batches and reduce the price)
Thru Axle Conversion system- TBD

What hole count is the Alfine Hub offered with?

The hub comes in 32 hole or 36 holes and just recently Shimano announced a 28 hole version but no release date as of yet. Most rims are typically 28 hole, therefore you should at a minimum, plan on purchasing a new rim. You will also need shorter spokes to accommodate the hub.

Are there other Internally Geared hubs beside Shimano?

Yes, there are several, however the only other hubs to consider in my opinion are the Rohloff and Kindernay which both cost around $1600 dollars. Unfortunately, both require two cables and two shifters to actuate/shift through the gears and is why I prefer the Alfine over both. The Kindernay truly works with thru axles while the Rohloff is thru axle compatible.

Do I have to use an internally geared hub with the B-DATS?

No, you can use the system with a conventional thru axle hub and single speed setup. I have not done this yet, but I would like to. If anyone is interested and think your ride might be a good candidate, please let me know.

How much does the system weigh?

The IGH and Belt Drive System will add roughly about a 1 lb. If you are converting from a typical 1x system. When converting from a 2x system you will typically shed a little weight. The hub itself is heavy (approx. 1665g), however you can’t just look at the weight of the hub alone, see comparison below:

see with and without comparison below:

What is the gear range of the hub?

The Alfine 11 speed Hub has a 408% range (.527-2.153). See chain/cog setup ranges below for comparison:

Are there bike manufacturers that offer belt drives on Full Suspension Mountain bikes?

Yes, there are only two bike manufacturers (that I know of) that offer a production full suspension MTB bike with a belt drive: Nicolai and Zeroed. However, what they offer is a totally different setup and is not a considered a conventional MTB. They are purpose-built bikes that use a Pinion gear box which replaces the conventional bottom bracket and requires a specifically designed frame to accept the gearbox. In addition, their rear geometry is altered significantly to make clearance for the belt.

Are there any other bicycle belt manufacturers beside Gates?

The only other bicycle belt manufacturer that I am familiar with is Veer. They have a novel design that uses a split belt that gets riveted together. This design allows it to fit on any bicycle, however the sprockets use a flange design to keep the belt centered on the sprocket resulting in an overall wider width of the sprocket of which is wider than that of the Gates. This combined with only larger size sprockets being currently available makes it only ideal for purpose-built commuter bikes.

What length belt do I need?

It depends on the bike, suspension travel, chain stay length/growth, pulley size and the fact that Gates belts are only available in certain lengths. and not available in 1 Tooth increments The three bikes listed above they use the following length belts:

Black Widow – 115T
Red Thunder – 113T
Scotty – 115T/118T

What gear ratios can I run?

Shimano recommends keeping the ratio of the front/rear sprocket as close to 1.9 as possible. Unfortunately due to the chain-line of the Alfine hub, the minimal amount of clearance available between the chain stay and front sprocket, and the limited amount of sprocket sizes available, this can hard to achieve. For the three setups listed above, I have been using a 39T Front Sprocket (Smallest size available in a 4 bolt 104 BCD) and 22T Rear sprocket which yields a ratio of 1.8.